Treatment of BALB/c-3T3 cells with PDGF induces them to selectively synthesize several proteins within 40-90 min. The selective synthesis of these proteins is blocked by inhibitors of RNA synthesis. A morphologically transformed variant of BALB/c-3T3 cells, which does not require or respon to PDGF, synthesizes these proteins constitutively providing evidence that these proteins regulate PDGF action. We propose that EGF and insulin, which are required for growth of PDGF-treated BALB/c-3T3 cells, stimulate PDGF-treated cells to selectively synthesize other proteins. One mechanism of cellular transformation may be the constitutive synthesis of such growth factor regulated gene products. A selection schema has been devised to allow the isolation of mutagenized BALB/c-3T3 cell variants which don't require either PDGF, EGF or insulin. These variants should be transformed and should constitutively synthesize the appropriate growth factor modulated gene products. Conversely, the isolation of variatns selected for morphologic transformation should yield clones that lack the requirement for one of these defined growth factors and constitutively synthesize the growth factor modulated proteins. The selective synthesis of PDGF-modulated proteins will be studied in detail. Antisera will be raised, and used to demonstrate identity of antigenic determinants between PDGF-modulated and constitutively synthesized proteins. An in vitro translation system will be utilized to demonstrate that PDGF regulates the level of translatable mRNA which specifies these proteins. To the best of our knowledge it has not previously been shown that polypeptide hormones regulate the amount of translatable mRNA.